1. Field of the Invention
The present invention relates to a method for manufacturing a sliding part for a hermetic compressor, and more particularly, to a method for manufacturing a sliding part for a hermetic compressor that is capable of improving an abrasion resistance of a sliding part and capable of shortening a manufacturing process.
2. Description of the Background Art
FIG. 1 is a sectional view of a general hermetic compressor.
In general, the hermetic compressor includes a hermetic case 6 in which a suction pipe 2 into which fluid is sucked from an external source and a discharge pipe 4 for discharging compressed fluid are connected, a drive unit 8 being disposed at a lower portion of the case 6 and generating a rotational force, and a compressing unit 10 being disposed at an upper portion of the case 6 and compressing the fluid according to the rotational force generated by the drive unit 8.
The drive unit 8 includes a stator 12 being disposed fixed at the inner circumference of the case 6, to which power is applied from an external source, a rotor 14 being disposed at an inner circumference of the stator 12 with a certain distance and rotated by electromagnetic interacting with the stator 12 when power is applied to the stator 12, and a crank shaft 18 being fixed at the rotor 14 and rotated accordingly and supported at a frame 16 fixed at the case 6.
The compression unit 10 includes a connecting rod 20 being connected to the upper end of the crank shaft 18 and making a reciprocating and linear movement according to a rotational movement of the crank shaft 18, a cylinder 22 being disposed fixed at an upper side of the frame 16 and having a space to which a fluid is provided, a piston 24 being connected to the connecting rod 20 for a linear movement together with the connecting rod 20, and slidably disposed inside the cylinder to compress fluid introduced into the cylinder, and a valve assembly 26 being mounted at one side of the cylinder 22 to supply fluid into the cylinder 22 and discharging a coolant compressed by the piston 24.
When such a hermetic compressor is driven for a fluid compression operation, friction is created between the crank shaft 18 and the frame 16, friction is created between the piston 24 and the inner wall of the cylinder 22, and friction is also created between the connecting rod 20 and the crank shaft 18.
Thus, the surface of sliding parts where friction is generated is to be surface-processed to increase lubrication and abrasion resistance.
A method for manufacturing a sliding part of a conventional art will now be described by taking an example of the piston 24.
The piston is manufactured by using a sintering and casting method for a mass production.
First, a method for manufacturing the piston 24 by sintering will now be described with reference to FIG. 2.
A material of ferrite group is pressed to form an exterior and subjected to sintering at a high temperature to obtain a compact organization and increase an adhesiveness between organizations (step S100).
After the sintering process, a steam treatment is carried out to maintain air tightness according to closure of pores formed in the organizations of the sintered product and increase corrosion resistance and abrasion resistance (step S200).
After the steam treatment, a roughing process is performed to process a shape of an inner and outer diameter (step S300).
After the roughing process, in order to improve a surface roughness of the sintered product, a sand blasting process is performed (step S400).
After the sand blasting process, in order to improve lubrication and abrasion resistance on a plastic deformation processed surface, a manganese phosphate coating treatment, a kind of lubricating treatment, is performed to form a coated layer 102 (step S500).
After the manganese phosphate coating process, molybdenum desulfidel treatment serving as a lubricant is carried to form a coated layer 104 at the surface of the piston (step S600).
According to a piston manufacturing method by a casting is that molten metal having a dissolved ferrite-group material is poured in a molding box to process a shape of a piston and then the same process as that of the piston manufacturing method by sintering as described above is performed to finally manufacture a piston.
The manganese phosphate coating process is a kind of phosphate coating process and performed for the purpose of a base of a paint, improvement of abrasion resistance, lubrication of plastic deformation process and electric insulation, for which phosphate solution of various metals is used suitable to the purpose.
For the molybdenum desulfide treatment process, a method is used in which the molybdenum desulfide(MoS2) is made to be powders or coated on a surface of the metal by mixing it with grease or oil.
After the piston manufacturing process of the conventional art is completed, as shown in FIG. 3, dual soft-coated layers 102 and 104 are formed at the surface of the piston by the manganese phosphate and molybdenum disulfide.
However, the coated layers 102 and 104 of the piston 24, the soft-coated layer, have a problem that as a predetermined time elapses, a gap (L) is generated due to a friction according to sliding with the cylinder 22, into which a coolant is leaked.
In addition, the conventional method for manufacturing a sliding part for a hermetic compressor has a problem that since the dual surface treatment process that the manganese phosphate treatment process and the molybdenum disulfide treatment process are subsequently performed is carried out, its production cost is increased, and especially, in case of the molybdenum disulfide surface processing, its unit cost is so high that its production cost is inevitably increased.
Moreover, because of the dual process performing the manganese phosphate treatment and the molybdenum disulfide treatment are subsequently performed, the thickness is increased due to the respective surface processing, causing exceeding the tolerance and the size deficiency occurs.
That is, When the thickness is increased in the surface treatment process of the piston, it is difficult to assembly the piston into the cylinder, and the fluid may be leaked due to the irregular surface of the piston in working.
Furthermore, due to the performing of the dual surface treatment of the piston, the size is changed when the piston and a piston pin are assembled, considerably degrading a combination rate, and it is difficult to compute a design size corresponding to the fact that the piston pin is released from the piston.
In addition, since the surface treatment process of the sliding part is dually performed, resultantly, the process is complicated, the manufacturing process duration is increased, and a defective generation rate is increased.
Therefore, an object of the present invention is to provide a method for manufacturing a sliding part for a hermetic compressor that is capable of simplifying a process and reducing a production cost and working time period by reducing a surface treatment process of a manufacturing process of a sliding part.
Another object of the present invention is to provide a method for manufacturing a sliding part for a hermetic compressor that is capable of facilitating assembling of sliding parts and improving a reliability in operation and abrasion resistance by minimizing a change in the thickness according to a surface treatment of the sliding parts and reducing a tolerance.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a method for manufacturing a sliding part for a hermetic compressor including the steps of: sintering a powder material of a ferrite group and forming a shape of a sliding part; performing a first stream treatment to close air pores formed in the organization of the sliding part after the sintering is finished; performing a roughing process to form an inner diameter and an outer diameter of the sliding part after the first steam treatment of the sliding part is finished; performing a sand blasting process to improve a surface roughness of the sliding part after the roughing process is finished; and performing a second steam treatment to form an oxide coated layer at the surface of the sliding part after the sand blasting process is finished.
In the method for manufacturing a sliding part for a hermetic compressor of the present invention, the step of performing a first steam treatment includes the steps of: conveying the sintering-finished sliding part into a stream furnace; and spraying stream which has been heated to a certain temperature to the conveyed sliding part to close the air pores of the sintered product.
In the method for manufacturing a sliding part for a hermetic compressor of the present invention, the step of performing a second stream treatment includes the steps of: conveying the sand blasting-finished sliding part into a stream furnace; and spraying stream which has been heated to a certain temperature to the surface of the conveyed sliding part to form an oxide coated layer on the surface of the sliding part.
In the method for manufacturing a sliding part for a hermetic compressor of the present invention, the temperature of the stream sprayed to the sliding part is about 500xc2x0 C.xcx9c600xc2x0 C.
To achieve the above object, there is also provided a method for manufacturing a sliding part for a hermetic compressor including the steps of: pouring a dissolved molten metal of a ferrite group in a molding box to create a cast in a certain form; performing a roughing process to form a shape of an inner diameter and an outer diameter of a cast product after the cast product is completely manufactured; performing a sand blasting process to improve a surface roughness of a sliding part after the roughing process is finished; and performing a stream treatment to form an oxide coated layer at the surface of the piston after the roughing process is finished.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.